One example of differential communication devices is known by the following patent document 1. The communication device disclosed in the patent document 1 has a terminal end portion and a communication completion detection portion, which are connected between two transmission lines. The terminal end portion includes a series circuit of a resistor and a capacitor. The communication completion detection portion detects completion of communication with other devices. When the communication completion detection portion detects the completion of communication, it connects the two transmission lines through the terminal end portion for a predetermined period from the completion of communication. Ringing is thus suppressed from arising on the transmission lines at the time of completion of communication.
According to a communication device disclosed in patent document 2, a diode is arranged between a positive-side output terminal and a negative-side output terminal of a transmission-side ECU, which are connected to two transmission lines, respectively. The diode is arranged so that its forward direction is from the negative-side output terminal to the positive-side output terminal. Ringing is thus reduced by shorting and suppressing a signal voltage changing in the negative direction by the diode.